runner/resultgen: Add cmdline to results.json

For easier repro scenarios, add the cmdline to the json: one can see the
exact command executed to try to reproduce a CI failure without needing
extra files.

Adding cmdline to the results.json doesn't need a version upgrade:
piglit can still parse the file.

Tested-by: Peter Senna Tschudin <peter.senna@linux.intel.com>
Reviewed-by: Peter Senna Tschudin <peter.senna@linux.intel.com>
Acked-by: Kamil Konieczny <kamil.konieczny@linux.intel.com>
Link: https://lore.kernel.org/r/20250207231039.2883195-12-lucas.demarchi@intel.com


Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>